Multi-scale simulation method for performance of two-dimensional magnetic material magnetic card

Abstract

The invention provides a multi-scale simulation method for the performance of a two-dimensional magnetic material magnetic card, and the method comprises the following steps: S1, selecting a two-dimensional ferromagnetic material from a two-dimensional material database, and obtaining a structure file of the two-dimensional ferromagnetic material; s2, carrying out structural optimization on the two-dimensional ferromagnetic material by utilizing first principle calculation, and obtaining a structural configuration with the lowest energy; s3, the magnetocrystalline anisotropy energy of the two-dimensional ferromagnetic material is calculated based on the force theorem; s4, different magnetic states are constructed based on the Heisenberg model to calculate magnetic exchange parameters; s5, the Curie temperature is obtained according to the magnetocrystalline anisotropy energy and the magnetic exchange parameters, and entropy change and temperature change values are calculated based on a Maxwell equation; s6, the relative refrigeration power is obtained by measuring the half broadening of the entropy change; and S7, calculating an inter-atomic second-order force constant and an inter-atomic third-order force constant, and calculating the lattice thermal conductivity in the two-dimensional magnetic material plane.

Description

Technical Field

[0001] The invention belongs to the technical field of solid-state refrigeration, and in particular relates to a multi-scale simulation method for magnetic card performance of two-dimensional magnetic materials. Background Art

[0002] The extensive use of fossil energy in industrial production, transportation and daily life has led to an increase in carbon dioxide emissions, which in turn exacerbates the greenhouse effect. In the global energy consumption structure, the refrigeration field accounts for a considerable proportion. According to statistics, about 30% of the world's electricity consumption is used in the refrigeration process. Therefore, refrigeration technology has become one of the important driving factors of the energy crisis, the greenhouse effect and the depletion of the ozone layer.

[0003] Compared with traditional gas compression refrigeration technology, solid-state refrigeration has become a green refrigeration solution that has attracted much attention due to its high energy efficiency and environmental friendliness. Solid-state refrigeration technology covers the magnetocaloric effect, electrocaloric effect, spring-clip effect and compression-clip effect. The magnetocaloric effect is the temperature change caused by the magnetic phase change of magnetic materials under the action of an external magnetic field. The research on the magnetocaloric effect has a long history. Since 1997, the research on the magnetocaloric effect has been carried out in bulk Gd 5 (Si 2 Ge 2 After the giant magnetocaloric effect near room temperature was first discovered in 2D ferromagnetic materials, a research boom in the field of magnetocaloric refrigeration was launched. 3 and CrGeTe 3 With the successful synthesis of 2D magnets, the research on two-dimensional magnetism has entered a new stage. Two-dimensional magnets have rich electrical, optical, mechanical and thermal properties, and exhibit novel physical phenomena such as magnetoelectric effect, magneto-optical effect and magnetoelastic effect, which make them have broad application prospects in the fields of spin electronics and magnetic storage devices. However, compared with other functional applications, the research on two-dimensional magnets in the field of magnetic refrigeration is still in a relatively early stage. Given the flexibility of two-dimensional magnets and their potential applications in mechanical deformation, their future development prospects in cooling technology are worth looking forward to. Summary of the invention

[0004] The purpose of this application is to provide a multi-scale simulation method for the magnetic card properties of two-dimensional magnetic materials, and to provide theoretical guidance for high-throughput screening of magnetic card materials with excellent comprehensive performance.

[0005] In order to achieve the above-mentioned objectives, one aspect of the present application provides a multi-scale simulation method for the magnetic properties of a two-dimensional magnetic material, comprising the following steps: S1: selecting a two-dimensional ferromagnetic material from a two-dimensional material database and obtaining a structural file of the two-dimensional ferromagnetic material; S2: optimizing the structure of the two-dimensional ferromagnetic material using first-principles calculations and obtaining a structural configuration with the lowest energy; S3: calculating the magnetocrystalline anisotropy of the two-dimensional ferromagnetic material based on the force theorem; S4: calculating magnetic exchange parameters by constructing different magnetic states based on the Heisenberg model; S5: obtaining the Curie temperature based on the magnetocrystalline anisotropy and magnetic exchange parameters, and calculating the entropy change and temperature change based on Maxwell's equations; S6: obtaining the relative cooling power by measuring the half-width of the entropy change; S7: calculating the second-order force constant and the third-order force constant between atoms, and calculating the lattice thermal conductivity within the plane of the two-dimensional magnetic material.

[0006] Preferably, S1 further includes:

[0007] The two-dimensional materials database is Computational 2D Materials Database (C2DB);

[0008] Materials with magnetic properties are selected from the two-dimensional material database and POSCAR structure files are exported.

[0009] Preferably, S2 also includes: using first-principles calculation software VASP to perform structural optimization, obtain the ground state crystal structure and find the crystal structure with the lowest energy.

[0010] Preferably, S3 also includes: S31: perform spin collinear static calculation to output wave function file WAVECAR and charge density file CHGCAR; S32: read WAVECAR and CHGCAR to perform spin non-collinear calculation, turn on spin-orbit coupling LSORBIT=T, LNONCOLLINEAR=T, LORBMOM=T, GGA_COMPAT=F, set NBANDS to twice that of spin collinear calculation, set SAXIS=001 and SAXIS=100 respectively to obtain two energies, E 100 -E 001 That is the magnetocrystalline anisotropy.

[0011] Preferably, S4 also includes: if the magnetic exchange parameters of the third nearest neighbor are calculated, a ferromagnetic state and three antiferromagnetic states are constructed by expanding the supercell, the energy of different magnetic states is calculated by VASP, and then an energy equation is established to calculate the exchange parameters.

[0012] Preferably, S5 also includes: bringing the magnetocrystalline anisotropy energy and magnetic exchange parameters into the Vampire atomic spin simulation software package, and obtaining the curves of magnetization intensity varying with external magnetic field and magnetization intensity varying with temperature, and obtaining the Curie temperature from the output file.

[0013] Preferably, S5 further includes: based on Maxwell's equations Calculate magnetic entropy change; based on Calculate the maximum temperature change; where ΔS mag is the magnetic entropy change, H is the magnetic field intensity, S is the entropy, T is the temperature, μ 0 is the vacuum magnetic permeability, M is the magnetization intensity, is the maximum temperature change, is the maximum magnetic entropy change, T c is the Curie temperature, c p For heat capacity.

[0014] Preferably, S6 further comprises: according to the change of entropy change with temperature, the half peak width δT FWHM It is defined as the temperature spread at half the maximum entropy change and is given by Resulting in the relative cooling power.

[0015] Preferably, S7 further comprises: calculating the second-order force constant between atoms by using a Phonopy software package, calculating the third-order force constant by using a Thirdorder software package, and calculating the lattice thermal conductivity within the plane of the two-dimensional magnetic material by using ShengBTE.

[0016] On the other hand, the present application provides a multi-scale simulation system for the magnetic card performance of a two-dimensional magnetic material, using the above method, including: a first acquisition module, configured to select a two-dimensional ferromagnetic material from a two-dimensional material database and obtain a structural file of the two-dimensional ferromagnetic material; a second acquisition module, configured to use first-principles calculations to optimize the structure of the two-dimensional ferromagnetic material and obtain a structural configuration with the lowest energy; a first calculation module, configured to calculate the magnetocrystalline anisotropy energy of the two-dimensional ferromagnetic material based on the force theorem; a second calculation module, configured to calculate magnetic exchange parameters by constructing different magnetic states based on the Heisenberg model; a third calculation module, configured to derive the Curie temperature based on the magnetocrystalline anisotropy energy and magnetic exchange parameters, and calculate entropy change and temperature change values ​​based on Maxwell's equations; a third acquisition module, configured to derive the relative cooling power by measuring the half-width of the entropy change; a fourth calculation module, configured to calculate the second-order force constant and the third-order force constant between atoms, and calculate the lattice thermal conductivity within the plane of the two-dimensional magnetic material.

[0017] The technical solution provided by this application can achieve the following beneficial effects:

[0018] 1. By combining spin collinearity and non-collinearity calculations, key magnetic characteristics such as magnetocrystalline anisotropy and magnetic exchange parameters are accurately calculated to fully reflect the magnetic properties of two-dimensional ferromagnetic materials;

[0019] 2. Using atomic spin dynamics simulation, we can intuitively show how the magnetization intensity changes with the external magnetic field and temperature, accurately predict the Curie temperature, and provide important support for the magnetic application of materials;

[0020] 3. Through strain engineering and carrier doping, study the regulation mechanism of external conditions on magnetic properties, and provide effective guidance and practical basis for the design optimization of magnetic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0022] Figure 1 is a schematic diagram of a multi-scale simulation method provided in an embodiment of the present application;

[0023] Figure 2 is a flow chart of the multi-scale simulation method provided in the embodiment of the present application;

[0024] Figure 3 This is a schematic diagram of the structure of the two-dimensional 1T-CrSX provided in the embodiment of the present application as an example;

[0025] Figure 4 is a flow chart of a method for optimizing the structure of a material provided in an embodiment of the present application;

[0026] Figure 5 is a flow chart of a method for calculating magnetocrystalline anisotropy energy provided in an embodiment of the present application;

[0027] Figure 6 is a schematic diagram of four magnetic states constructed according to the embodiments of the present application;

[0028] Figure 7 is a graph showing the entropy change and temperature change of the CrSC1 material provided in the embodiment of the present application as a function of temperature;

[0029] Figure 8 This is a schematic diagram of the strain engineering and carrier doping provided in the embodiment of the present application to control the Curie temperature and entropy change;

[0030] Fig. 9 is a schematic diagram of the structure of a multi-scale simulation system provided in an embodiment of the present application;

[0031] Among them: a first acquisition module 10 , a second acquisition module 20 , a first calculation module 30 , a second calculation module 40 , a third calculation module 50 , a third acquisition module 60 and a fourth calculation module 70 . DETAILED DESCRIPTION

[0032] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0033] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0034] This application proposes a multi-scale simulation method for the magnetic properties of two-dimensional magnetic materials. Figure 1 As shown, in the hope of finding a magnetic refrigeration material with a large entropy change in a two-dimensional magnetic material, the described implementation case is only a part of the present invention, not all implementation cases. It should be noted that in the specific implementation method, the software calculation part involved is calculated using the VASP, Vampire, Phonopy and ShengBTE programs commonly used in the industry to efficiently and accurately obtain the data in each step of the present invention.

[0035] In one example, if Figure 2 As shown, the multi-scale simulation method includes the following steps S1-S7:

[0036] S1: Select a two-dimensional ferromagnetic material from a two-dimensional material database, and obtain a structure file of the two-dimensional ferromagnetic material.

[0037] It can be imagined that the two-dimensional material database can be selected from Computational2D Materials Database (C2DB), log in to the two-dimensional material database (C2DB), select a material with magnetism, that is, a two-dimensional ferromagnetic material, export the POSCAR structure file, and view its crystal structure through Vesta. Its crystal structure is as follows Figure 3 to facilitate first-principles calculations.

[0038] It is understandable that, according to the research needs, screening conditions can be further used, such as the crystal type, symmetry, band gap, magnetization intensity, etc. of the material, to narrow the screening range and determine the two-dimensional ferromagnetic materials that meet the requirements.

[0039] After importing the POSCAR structure file into Vesta, the crystal structure of the material can be observed in the Vesta interface, including the symmetry of the unit cell, atomic arrangement, interlayer distance and other information. The crystal structure can be rotated, enlarged or reduced as needed to facilitate intuitive observation of the geometric properties of the material.

[0040] Based on the POSCAR structure file and the crystal structure confirmed by Vesta software, the initial parameters required for the first-principles calculation are set, including but not limited to unit cell parameters (such as lattice vectors), atomic coordinates and element types, calculation model type (such as spin polarization calculation) and exchange-correlation function selection (such as GGA+U).

[0041] S2: Utilize first-principles calculations to optimize the structure of the two-dimensional ferromagnetic material and obtain the structural configuration with the lowest energy.

[0042] The optimization process is as follows Figure 4 As shown, S21: prepare calculation input files for structure optimization, including POSCAR file, POTCAR file, KPOINTS file and INCAR file.

[0043] According to the atomic species involved in the POSCAR structure file, select the appropriate POTCAR file from the pseudopotential library provided by VASP. You can choose a pseudopotential file based on the PBE (Perdew-Burke-Ernzerhof) functional for density functional theory calculations.

[0044] KPOINTS file: sets the k-point grid for integration in reciprocal space; the k-point grid can be generated using the Monkhorst-Pack method, and the appropriate k-point density can be selected based on the unit cell size. For example, for a two-dimensional material, the typical setting for the k-point grid is k-points = 11 × 11 × 1, where the z direction is set to 1 to accommodate the two-dimensional nature of the material.

[0045] INCAR file: Configure the control parameters required for VASP operation, the specific settings are as follows: PREC = Accurate, set the high-precision calculation mode; ISIF = 3, allow simultaneous optimization of the unit cell volume, shape and atomic position; ENCUT = 500eV, set the plane wave cutoff energy; EDIFF = 1E-6, set the electronic iteration convergence criterion; IBRION = 2, select the conjugate gradient method for geometry optimization; NSW = 100, set the maximum number of optimization steps to 100 steps; ISPIN = 2, turn on spin polarization calculation; MAGMOM = N × μ, initialize the magnetic moment of each atom according to the properties of ferromagnetic materials.

[0046] S22: Perform structure optimization calculations. Place the POSCAR, POTCAR, KPOINTS, and INCAR files together in the VASP running directory. Run VASP using the following command: mpirun -np 32vasp_std>output.log, where -np 32 indicates the use of 32 cores for parallel calculations, and vasp_std is the standard version of the VASP executable file. VASP automatically iterates and optimizes the structure, gradually approaching the ground state crystal structure by reducing interatomic forces and total energy.

[0047] S23: Check and extract the optimization results, and confirm in the output file OUTCAR or OSZICAR whether the calculation has reached the convergence criterion. The convergence condition is: the interatomic force is less than The total energy change is less than 1E-6eV.

[0048] After the optimization is completed, VASP will generate a CONTCAR file, which records the unit cell parameters and atomic coordinates of the ground state crystal structure, and rename CONTCAR to POSCAR for subsequent calculations.

[0049] S24: Verify the stability of the ground state crystal structure. Through further static energy calculation, confirm that the optimized structure is the lowest energy state. Keep the geometric structure unchanged, set NSW = 0, perform static calculations, and record the total energy (E_TOT). If the total energy is consistent with the lowest energy recorded during the optimization process, it can be confirmed that the structure is the ground state crystal structure.

[0050] S25: Save the optimization results and save the final CONTCAR file as the standard description file of the ground state crystal structure for subsequent calculations. At the same time, save the output files (OUTCAR, OSZICAR, etc.) for record and reference.

[0051] Through the steps in the above example, the VASP software based on density functional theory can be used to optimize the structure of two-dimensional ferromagnetic materials and obtain the ground state crystal structure with the lowest energy. The optimized crystal structure provides the basis for subsequent magnetism, electronic structure, energy band calculation and multi-scale simulation.

[0052] S3: Calculate the magnetocrystalline anisotropy energy of the two-dimensional ferromagnetic material based on the force theorem.

[0053] The calculation process of magnetocrystalline anisotropy energy is as follows Figure 5 As shown, S31: perform spin collinear static calculation to output wave function file WAVECAR and charge density file CHGCAR.

[0054] Specifically, execute the following command: mpirun-np 32vasp_std>output.log. After the calculation is completed, the wave function file WAVECAR, the charge density file CHGCAR and the calculation output file OUTCAR are generated. Among them, WAVECAR records the spin collinearity calculation results, CHGCAR is used to describe the electronic distribution state of the material, and OUTCAR contains energy, magnetic moment and convergence information. After confirming the calculation convergence, back up the WAVECAR and CHGCAR files for subsequent spin non-collinear calculations.

[0055] S32: Read WAVECAR and CHGCAR for spin non-collinear calculation, turn on spin-orbit coupling LSORBIT=T, LNONCOLLINEAR=T, LORBMOM=T, GGA_COMPAT=F, set NBADS to twice that of spin collinear calculation, set SAXIS=001 and SAXIS=100 to get two energies, E 100 -E 001 That is the magnetocrystalline anisotropy.

[0056] Specifically, for the directions of SAXIS=001 and SAXIS=100, execute the following commands respectively: mpirun-np32vasp_ncl>output_001.log, mpirun-np 32vasp_ncl>output_100.log, where vasp_ncl is a VASP version that supports non-collinear computing.

[0057] Look up the free energy (F=E-TS) value in the OUTCAR file. For calculations with SAXIS=001, record the energy as E 001 For calculations with SAXIS = 100, record the energy as E 100 , E 100 -E 001This is the magnetocrystalline anisotropy energy. If the result is positive, it indicates that the magnetic material has higher stability in the 001 direction; if it is negative, the 100 direction is more stable. Save the calculation results as an analysis report, including free energy, magnetic moment, and magnetocrystalline anisotropy energy parameters.

[0058] Through this example, using the spin collinear and non-collinear calculation methods, combined with the spin-orbit coupling and the settings of different quantization axis directions, the magnetocrystalline anisotropy energy of two-dimensional ferromagnetic materials can be accurately calculated. This characteristic provides a theoretical basis for understanding the origin of material magnetism and designing new magnetic devices.

[0059] S4: Construct different magnetic states based on the Heisenberg model to calculate the magnetic exchange parameters.

[0060] Specifically, construct ferromagnetic and antiferromagnetic states, calculate the energies of different magnetic states. If considering calculating the magnetic exchange parameters up to the third nearest neighbor, one ferromagnetic state and three antiferromagnetic states need to be constructed. Among them, use the optimized ground state crystal structure file to construct the ferromagnetic state, and the three antiferromagnetic states are the arrangements where the spins of the nearest neighbor atoms are reversed, the spins of the next-nearest neighbor atoms are reversed, and the spins of the third-nearest neighbor atoms are reversed.

[0061] In POSCAR, construct the antiferromagnetic state by adjusting the arrangement of magnetic atoms in the crystal, and at the same time update the MAGMOM parameter in the INCAR file to reflect the spin distribution.

[0062] Use VASP to perform self-consistent calculations on the ferromagnetic state and the three antiferromagnetic states respectively to obtain their energies. Run the self-consistent calculations for the ferromagnetic state and the three antiferromagnetic states respectively. After the calculation is completed, extract the total energy of the system from the OUTCAR file.

[0063] Substitute into the Heisenberg model for equation solving. The formula is:

[0064]

[0065] As Figure 6 shown, different colors represent the spin-up and spin-down states respectively. The equation form constructed with 1T-CrSX as an example is as follows:

[0066] -48J 1 S 2 -48J 2 S 2 -48J 3 S 2 +E 0 =E FM ;

[0067] 16J 1 S 2 -16J 2 S 2+24J 3 S 2 +E 0 =E AFM1 ;

[0068] 16J 1 S 2 +16J 2 S 2 -48J 3 S 2 +E 0 =E AFM2 ;

[0069] -16J 1 S 2 +16J 2 S 2 +16J 3 S 2 +E 0 =E AFM3 ;

[0070] By comparing J 1 , J 2 , J 3 to analyze the strength of the magnetic coupling and its physical mechanism among the nearest neighbor, next-nearest neighbor, and third-nearest neighbor.

[0071] By constructing different magnetic states and combining with the Heisenberg model to solve the magnetic exchange parameters, the magnetic interactions of two-dimensional magnetic materials can be deeply understood, providing a theoretical basis for optimizing material properties and designing new magnetic materials.

[0072] S5: Obtain the Curie temperature based on the magnetocrystalline anisotropy energy and magnetic exchange parameters, and calculate the entropy change and temperature change values based on Maxwell's equations.

[0073] Substitute the magnetocrystalline anisotropy energy calculated in S3 and the exchange interaction calculated in S4 into the Vampire atomic spin simulation software package. By performing atomic spin dynamics simulations, the curves of magnetization M versus external magnetic field H and magnetization M versus temperature T can be obtained, and the magnitude of the Curie temperature can be read from the M-T curve.

[0074] Based on Maxwell's equations the magnitude of the maximum magnetic entropy can be obtained. Using the maximum temperature change can be obtained. Using Maxwell's relations to process the M-T curve, the curves of entropy change and temperature change versus temperature can be obtained as shown in Figure 7 .

[0075] S6: Obtain the relative refrigeration power by measuring the half-width of the entropy change.

[0076] The entropy change with temperature is calculated in S5, and the half-peak width is defined as the temperature broadening at half the maximum entropy change. The relative cooling power can be obtained.

[0077] S7: Calculate the second-order and third-order force constants between atoms, and calculate the lattice thermal conductivity within the plane of the two-dimensional magnetic material.

[0078] The second-order force constants between atoms are calculated using the Phonopy software package, the third-order force constants are calculated using the Thirdorder software package, and the lattice thermal conductivity within the plane of the two-dimensional magnetic material is calculated using ShengBTE. The two-dimensional material needs to be corrected.

[0079] Specifically, the second-order force constant file and the third-order force constant file are converted into the format supported by ShengBTE, the input file of ShengBTE is created, and the key parameters are set to perform the ShengBTE calculation. After the calculation is completed, an output file is generated, which contains the lattice thermal conductivity of the two-dimensional material in different directions.

[0080] In the output file, read the thermal conductivity value parallel to the lattice (x, y direction), average the lattice thermal conductivity in the two directions, and get the in-plane lattice thermal conductivity. It should be noted that some lattice thermal conductivities are isotropic and some are anisotropic. You can choose the one you need.

[0081] By calculating the second-order and third-order force constants between atoms through Phonopy and Thirdorder, and combining ShengBTE to calculate the lattice thermal conductivity, the accurate value of the in-plane lattice thermal conductivity of the two-dimensional magnetic material can be obtained.

[0082] S8: Perform strain engineering and carrier doping on the material. Strain engineering only requires modifying POSCAR and scaling the in-plane lattice vectors. Carrier doping only requires modifying the NELECT parameters in INCAR. Repeat S2 to S4 to obtain the magnetic exchange parameters and magnetocrystalline anisotropy. Then perform a Monte Carlo simulation. According to the potential energy difference method, it is only necessary to simulate the conditions under zero magnetic field and 5T magnetic field. The total energy obtained under 5T magnetic field minus the magnetic field energy is the potential energy dE. The work done W = 0.5*H*(Mz-Mz0), H is the external magnetic field intensity, Mz is the magnetic moment in the z direction under 5T magnetic field, and Mz0 is the magnetic moment in the z direction under zero magnetic field. Entropy change ΔS = (W-dE) / T. As Figure 8 shown.

[0083] Specifically, the in-plane lattice vectors of the POSCAR file are scaled, the strain value ε is set (e.g., -5%, -2%, 0, +2%, +5%, etc.), the scaling factor S=1+εS is calculated and the lattice vector is modified. For example, the original lattice vector is: a1=[a 11 ,a12 ,a 13 ],a2=[a 21 ,a 22 ,a 23 ], the lattice vector after strain is: a 1 ′=S·a 1 , a 2 ′=S·a 2 , update the corresponding lattice vector in POSCAR.

[0084] It is conceivable that for a plurality of strain values ​​(eg, -5% to +5%), the POSCAR file is modified to generate a set of crystal structures.

[0085] In the INCAR file, modify the NELECT parameter to control carrier doping. When doping electrons, the number of electrons increases; when doping holes, the number of electrons decreases.

[0086] It is conceivable that for multiple doping concentrations (e.g., -0.2e- / A° 2 To +0.2e- / A° 2 ) to set the NELECT parameters in INCAR respectively.

[0087] For each strain value and carrier doping concentration, repeat S2 to S4 to obtain the magnetic exchange parameters and magnetocrystalline anisotropy. Then perform Monte Carlo simulation. According to the potential energy difference method, it is only necessary to simulate the conditions under zero magnetic field and 5T magnetic field. The total energy obtained under 5T magnetic field minus the magnetic field energy is the potential energy dE. The work done W = 0.5*H*(Mz-Mz0), H is the external magnetic field intensity, Mz is the magnetic moment in the z direction under 5T magnetic field, and Mz0 is the magnetic moment in the z direction under zero magnetic field. Entropy change ΔS = (W-dE) / T.

[0088] Through strain engineering and carrier doping, the magnetocrystalline anisotropy and thermal properties of two-dimensional magnetic materials can be regulated, further revealing their physical mechanisms and providing support for the design of high-performance magnetic and thermal management materials.

[0089] Based on the first principles, Monte Carlo simulation, magnetic card thermodynamics and other methods, the key magnetic card performance parameters of two-dimensional magnetic materials, isothermal entropy change, adiabatic temperature change, relative cooling power, and thermal conductivity are calculated. The magnetic card performance can be regulated by strain engineering and carrier doping. This application provides a set of methods for comprehensively calculating magnetic card performance parameters and quickly calculating entropy change values, providing theoretical guidance for high-throughput screening of magnetic card materials with excellent comprehensive performance.

[0090] In one example, 1T-CrSCl was selected as a two-dimensional ferromagnetic material to calculate the magnetic properties of 1T-CrSCl. First, the structure of 1T-CrSCl was obtained from C2DB, and then the structure was optimized and self-consistently calculated. Then the magnetocrystalline anisotropy energy was calculated, and then four magnetic states were constructed to calculate the magnetic exchange parameters. a is the lattice constant, J is the lattice constant, and 1 , J 2 , J 3 are the nearest neighbor, next nearest neighbor and next nearest neighbor magnetic exchange parameters, MAE is the magnetocrystalline anisotropy energy, FM is the ferromagnetic state energy set to 0, AFM1, AFM2, AFM3 are the energy differences between antiferromagnetic state 1, antiferromagnetic state 2, antiferromagnetic state 3 and the ferromagnetic state, respectively. The obtained magnetic data are shown in Table 1 below.

[0091]

[0092] Table 1

[0093] The magnetic card performance parameters of CrSCl obtained from the Maxwell relationship are shown in Table 2 below. c is the Curie temperature, is the maximum magnetic entropy change under 5T magnetic field, is the maximum adiabatic temperature change under 5T magnetic field, RCP is the relative cooling power, Q is the cooling capacity, C P is the heat capacity, κ L is the thermal conductivity at Curie temperature.

[0094]

[0095] Table 2

[0096] Based on the potential energy difference method, the magnetic data under strain engineering and carrier doping and the magnetic card performance parameters are shown in Table 3 and Table 4 respectively.

[0097]

[0098] Table 3

[0099]

[0100] Table 4

[0101] like Fig. 9 As shown, this example provides a multi-scale simulation system 1 for the magnetic card properties of two-dimensional magnetic materials, using the multi-scale simulation method provided by any of the above examples. The system includes a first acquisition module 10, a second acquisition module 20, a first calculation module 30, a second calculation module 40, a third calculation module 50, a third acquisition module 60 and a fourth calculation module 70.

[0102] Specifically, the first acquisition module 10 is configured to select a two-dimensional ferromagnetic material from a two-dimensional material database and obtain a structural file of the two-dimensional ferromagnetic material; the second acquisition module 20 is configured to use first-principles calculations to perform structural optimization on the two-dimensional ferromagnetic material and obtain a structural configuration with the lowest energy; the first calculation module 30 is configured to calculate the magnetocrystalline anisotropy energy of the two-dimensional ferromagnetic material based on the force theorem; the second calculation module 40 is configured to calculate the magnetic exchange parameters by constructing different magnetic states based on the Heisenberg model; the third calculation module 50 is configured to obtain the Curie temperature based on the magnetocrystalline anisotropy energy and the magnetic exchange parameters, and calculate the entropy change and temperature change values ​​based on Maxwell's equations; the third acquisition module 60 is configured to obtain the relative cooling power by measuring the half-width of the entropy change; the fourth calculation module 70 is configured to calculate the second-order force constant and the third-order force constant between atoms, and calculate the lattice thermal conductivity within the plane of the two-dimensional magnetic material.

[0103] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A multi-scale simulation method for the magnetic card performance of a two-dimensional magnetic material, characterized in that: The following steps are involved: S1: selecting a two-dimensional ferromagnetic material from a two-dimensional material database, and obtaining a structure file of the two-dimensional ferromagnetic material; S2: Optimizing the structure of the two-dimensional ferromagnetic material using first-principles calculations and obtaining a structural configuration with the lowest energy; S3: Calculating the magnetocrystalline anisotropy energy of the two-dimensional ferromagnetic material based on the force theorem; S4: Construct different magnetic states based on the Heisenberg model to calculate magnetic exchange parameters; S5: deriving the Curie temperature according to the magnetocrystalline anisotropy energy and the magnetic exchange parameter, and calculating the entropy change and temperature change values ​​based on Maxwell's equations; S6: Determine the relative cooling power by measuring the half width of the entropy change; S7: Calculate the second-order and third-order force constants between atoms, and calculate the lattice thermal conductivity within the plane of the two-dimensional magnetic material.

2. The multi-scale simulation method according to claim 1, characterized in that: S1 also includes: The two-dimensional materials database is Computational 2D Materials Database (C2DB); Materials with magnetic properties are selected from the two-dimensional material database and POSCAR structure files are exported.

3. The multi-scale simulation method according to claim 1, characterized in that: S2 also includes: The first-principles calculation software VASP was used to optimize the structure, obtain the ground state crystal structure and find the crystal structure with the lowest energy.

4. The multi-scale simulation method according to claim 1, characterized in that: S3 also includes: S31: Perform spin collinear static calculation to output wave function file WAVECAR and charge density file CHGCAR; S32: Read WAVECAR and CHGCAR for spin non-collinear calculation, turn on spin-orbit coupling LSORBIT=T, LNONCOLLINEAR=T, LORBMOM=T, GGA_COMPAT=F, set NBADS to twice that of spin collinear calculation, set SAXIS=001 and SAXIS=100 to get two energies, E 100 -E 001 That is the magnetocrystalline anisotropy.

5. The multi-scale simulation method according to claim 1, characterized in that: S4 also includes: If the magnetic exchange parameters of the third nearest neighbor are calculated, after expanding the supercell, a ferromagnetic state and three antiferromagnetic states are constructed, the energies of different magnetic states are calculated by VASP, and then the energy equation is established to calculate the exchange parameters.

6. The multi-scale simulation method according to claim 1, characterized in that: The S5 also includes: The magnetocrystalline anisotropy energy and magnetic exchange parameters are introduced into the Vampire atomic spin simulation software package, and the curves of magnetization intensity varying with external magnetic field and magnetization intensity varying with temperature are obtained, and the Curie temperature is obtained from the output file.

7. The multi-scale simulation method according to claim 1, characterized in that: The S5 also includes: Based on Maxwell's equations Calculate magnetic entropy change; based on Calculate the maximum temperature change; Among them, ΔS mag is the magnetic entropy change, H is the magnetic field intensity, S is the entropy, T is the temperature, μ0 is the vacuum permeability, M is the magnetization intensity, is the maximum temperature change, is the maximum magnetic entropy change, T c is the Curie temperature, c p For heat capacity.

8. The multi-scale simulation method according to claim 6, characterized in that: The S6 also includes: According to the change of entropy with temperature, the half-peak width δT FWHM It is defined as the temperature spread at half the maximum entropy change and is given by Resulting in the relative cooling power.

9. The multi-scale simulation method according to claim 1, characterized in that: The S7 also includes: The second-order force constants between atoms are calculated using the Phonopy software package, the third-order force constants are calculated using the Thirdorder software package, and the lattice thermal conductivity within the plane of the two-dimensional magnetic material is calculated using ShengBTE.

10. A multi-scale simulation system for the magnetic card performance of two-dimensional magnetic materials, characterized in that: The multi-scale simulation method according to any one of claims 1 to 9 comprises: A first acquisition module is configured to select a two-dimensional ferromagnetic material from a two-dimensional material database and acquire a structure file of the two-dimensional ferromagnetic material; A second acquisition module is configured to optimize the structure of the two-dimensional ferromagnetic material by using first-principles calculations and obtain a structural configuration with the lowest energy; A first calculation module is configured to calculate the magnetocrystalline anisotropy energy of the two-dimensional ferromagnetic material based on the force theorem; A second calculation module is configured to construct different magnetic states based on the Heisenberg model to calculate magnetic exchange parameters; A third calculation module is configured to obtain the Curie temperature according to the magnetocrystalline anisotropy energy and the magnetic exchange parameter, and calculate the entropy change and temperature change values ​​based on Maxwell's equations; A third acquisition module is configured to obtain a relative cooling power by measuring a half width of the entropy change; The fourth calculation module is configured to calculate the second-order force constant and the third-order force constant between atoms, and calculate the lattice thermal conductivity within the plane of the two-dimensional magnetic material.

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